1. Field of the Disclosure
The present disclosure relates generally to a receiver and a reception method in a wireless communication system and, more particularly, to an apparatus and method for performing channel estimation using a Low-Pass Filter (LPF) capable of adaptively adjusting its filter order and bandwidth in a wireless communication system.
2. Description of the Related Art
With the standardization and commercialization of high-speed mobile communication systems such as Wideband Code Division Multiple Access (WCDMA) and High Speed Downlink Packet Access (HSDPA), various types of equalizer-based receivers suitable for high-speed reception have been studied and developed. An equalizer-based receiver includes a channel estimator that estimates a channel and an equalizer that performs channel equalization using the estimated channel. The equalizer selects a weight to improve a Signal to Noise Ratio (SNR) and compensate for multipath interference and Inter Symbol Interference (ISI). The equalizer corrects distortion and generates an estimate of a transmitted symbol. Since a weight for channel equalization is generated from an estimated channel, the overall system performance may depend on the accuracy of the estimated channel and a method of generating the weight of channel equalization.
In general, a LPF eliminates noise by adjusting a bandwidth of a passband according to a bandwidth of a signal delivered thereto, and conventionally a method of eliminating noise using a first-order LPF has been used. For example, noise components other than a noise component within a bandwidth of a pilot signal for channel estimation may be eliminated through a first-order LPF.
However, when a first-order LPF is used, noise components cannot be efficiently eliminated as compared to a higher-order LPF, because a transition width interval is relatively larger than that of a higher-order LPF and a transfer function of the first-order LPF filter has a gentle slope in a transition width, which may cause performance degradation.
In contrast, a higher-order LPF (e.g., an order higher than that of a first-order LPF) may have larger group delay than a first-order LPF. Group delay refers to a time from when a signal is input into an LPF to when the signal is output from the LPF.
In the related art, only a first-order LPF is used because group delay cannot be adaptively compensated for in a higher-order LPF, and thus the filtering performance degrades in an environment in which lots of noise is present or a Doppler spread is large.